1. Field of Invention
This invention relates to an image forming device such as a transfer type copying machine, etc.
2. Description of the Prior Art
In the conventional transfer type electrophotographic devices, photosensitive changes occur if photosensitive elements are left without using them for many hours. Such sensitivity changes include long-term changes such as deterioration in response in relation to the life of photosensitive elements and so on as well as temporary ones attributable to moisture absorption, influence of residual surface charge and irregularities in sensitivity due to leak light, etc. As a means of solving these problems, it has been proposed, prior to proceeding to a process sequence, to provide a photosensitive element with light beforehand for a specified time and, in so doing, cause it to rotate so as to maintain the sensitivity (response) of the photosensitive element at a certain level or make it uniform.
However, especially when preliminary exposure is performed for many hours directly before the commencement of a first sheet cycle, or when it is performed with a strong light source, there has been a possibility of an initial deterioration of the photo-sensitive characteristics (response) of the photosensitive material due to a fatigue of the rotating photosensitive element, resulting in the deterioration of the latent image of the first sheet.
Further, there has also been such a possibility when a strong light source is employed to eliminate a residual image after transfer. On the other hand, however, if pre-exposure is started before a fixed time of image formation and image exposed during pre-exposure, an image may be formed at the boundary between preexposed and non-preexposed planes, resulting in the possibility of irregularities being produced in the first sheet.
Further, in cases where preexposure as mentioned above and postexposure after image formation are carried out in a small copying apparatus, the distance between the document platen glass, optical system, photosensitive element, etc. and the light sources for pre- and post-exposure is made shorter and there is the possibility of the platen glass, etc. being heated and broken due to temperature rise of the light sources.
Such possibility has been greater especially in the case of a compact type apparatus where bar lens or optical fiber is employed as the optical system for image exposure on the rotating photosensitive element due to the extreme proximity of the platen glass to the rotating photosensitive element. Further, there has been a danger especially when strong halogen lamps are employed as light sources for pre- and post-exposure.
On the other hand, when making the transfer type apparatus smaller in size, it is necessary to provide essential means for the execution of the process in quite close order and accordingly, so that providing the means for pre- and post-treatment of the photosensitive element makes the apparatus more complicated and causes inconvenience of maintenance; for such reasons, real miniaturization has almost been hopeless.
On the other hand, there has been an apparatus in which the rotating element contributing to transfer is rotated, after power-on to the apparatus, for pre-exposure or cleaning.
On the other hand, in ordinary copying apparatuses, if power is switched on prior to the beginning of use, the apparatus itself diagnoses as to whether the condition suitable for copying is existing and no copying is effected if various requirements are not met. Such requirements include the availability of transfer material, developer and key counter, etc. and heater temperature at the fixing roller, etc. Especially, the temperature of the fixing roller at the time of power switch ON is not at a temperature making fixing possible nearly at each time.
Accordingly, if rotation of the rotating body is caused to follow various factors mentioned above, rotation time or number of rotations may extend over many hours and for this reason, there has been the possibility of deterioration of photosensitivity as previously mentioned or damage to the surface of the rotating body. In addition, standby time till the commencement of exposure becomes long, resulting in impeding speedup of copying work.
Further, it has hitherto been known that in a transfer type of copying apparatus, if a jammed sheet condition is detected, all the sheet feed members inclusive of the rotating body and fixing rollers, etc. are stopped so as to prevent a further aggravated condition of jammed sheet.
In such a case, jamming occurs mostly during a copy cycle and therefore the electric potential at the rotating body is not uniform. Especially, on the surface of the rotating body from the charger to the discharger such as light source, etc. downstream in the direction of rotation of the rotating body, charge from the charger remains and the machine is left in such condition. Such residual charge remain as memory on the rotating body and may produce mottle on the first sheet at the time of resumption of copying.
Further, in the past, when stopping the operation of an apparatus on detection of jamming of a sheet, a mechanical lock was applied so as to prevent operation of the apparatus till completion of elimination of jamming and therefore, unlocking of such lock was troublesome and the device for such unlocking was quite expensive.
In addition, elimination of jamming was carried out by opening the casing of the apparatus, but even if the casing was not closed completely after elimination of jamming, the apparatus happened to restart running in some cases, bringing about quite a dangerous condition.
On the other hand, it has hitherto been known, in a copying apparatus equipped with copying setting switches such as number of copy sheets setting key switch, copy start switch and copy stop key switch, etc., to provide segment indicators and lamps, etc. to let the operator know that various key switches were pressed and the signals accepted by the control unit provided in the inside. Further, it is already known to employ indication means such as lamps and light emission diodes, etc. for the purpose of alarm at the time of failure such as jamming at a copying apparatus. However, these two systems, if employed in a copying apparatus, caused an increase of costs or made the control and indication units of a copying apparatus complicated. Moreover, it often took time to judge the contents of indication, resulting in a loss of copying time.